Spectrum

Last Thursday, September 17, we held a workshop on Spectrum. Though I may be slightly biased (and very geeky), I thought it was the coolest workshop to date. Where else can you have well-informed people disagree so starkly on such key issues as the need for more licensed spectrum (some say we need it now, others that we still have a lot of idle capacity) and sources of that spectrum (some say the government, others point to specific commercial users)? At what other workshop have panelists thrown out such cool terms as "White-Fi" and "self-optimizing networks," then actually been able to explain their application to the real world?

Though it's nearly impossible to capture the essence of such a rich discussion, I drew 3 conclusions from the workshop.

1. The usage of wireless broadband services is growing at a faster rate than technological advances and other innovations to make more efficient use of spectrum. At some point, therefore, we will face a spectrum supply-demand imbalance.

2. There are numerous approaches to address the supply-demand imbalance, all of which are important and none of which can alone solve the problem:

A complete, dynamic database of current occupants, licensed and unlicensed, by time, geography, and frequency, would help bring transparency to the marketplace.

Building on this database, a well-functioning secondary market would facilitate movement of spectrum licenses to their most productive uses.

Investment in and commercialization of innovative new technologies will continue to deliver more efficient and economic usage of existing spectrum allocations.

We can only squeeze so much juice out of the orange, so to speak. We will need to find additional sources of spectrum to allocate to wireless broadband services to meet growing demand.

3. Finally, wireless broadband service is critical to solving our broadband deployment and adoption challenges - we need to start working on solving the spectrum supply-demand imbalance today, even if it won't reach "crisis" stage until some point in the future. Coleman Bazelon, one of the panelists, summarized the importance best when he said that no other current commercial usage of spectrum delivers as much economic value as wireless broadband service (I paraphrase, of course).

Another point came across clearly during the workshop: we can learn a lot about using spectrum more efficiently from the explosion of devices and applications in unlicensed spectrum, and from non-commercial use of cognitive radios and ad hoc networking driven by DARPA for military applications.

Like any animated discussion, though, the workshop also raised more questions in my mind:

How much additional spectrum will we need for wireless broadband service to close the supply-demand gap?

By when will we need this additional spectrum?

From whom do we get this additional spectrum? How?

What policies will enable continued innovation in spectrum efficiency and migration towards more productive uses of spectrum? What policies would hurt?

I'm very interested to read what others think about the spectrum challenges and opportunities we face today. I encourage you to engage in this process by continuing the discussion thread on the blog or by filing comments with ECFS Express (or our standard submission page if you need to attach a file). You can also file comments responding to the Wireless Innovation NOI using the same docket number, 09-51. Thanks in advance for your input!

2 Responses to “Spectrum”

I found this workshop very informative and enlightening. Here are some of the statements made by industry representatives. I checked the recording, so I believe these statements are accurate:
* Spectrum can deliver ~1-2Mbps per hertz (larger blocks are more efficient; note: some references state up to 5Mbps/hz for WiMAX)
* Need to find about 1280mhz of spectrum by 2020 timeline (ITU/2007), probably sooner
* Spectrum needs to be in contiguous blocks and free of encumbrances (interference, restrictions) for effective deployment and cost management
* Real variable: usage/customer - emerging hungry applications such as video; as more users adopt these, more spectrum is needed
* Current WiMAX mobile users are using 1Gb/month, expect to grow to 15Gb+/month with more streaming real-time services
* Current laptop users (non-WiMAX) with data cards are currently using 1-5Gb/month
* Need 20mhz channels per sector for WiMAX, which means 120Mhz on a tower with two carriers and three sectors
* Typical number of subscribers per cell tower: 1000 in rural markets, 660 in dense areas; typical requirement: 1 to 5 Mbps per subscriber
* Given a choice, 802.11n Wi-Fi is faster and better than WiMAX/30mhz
* The carriers do not perceive there to be any fundamental reliability issues with wireless service - occasional problems occur due to spectrum shortages
* Download vs. upload ratio is increasing to somewhere around 70%/30%
* High upload bandwidth becomes a challenge for mobile devices powered by batteries
* Need a minimum of 30Mbps at the tower for 4G WiMAX
* Verizon plans to re-use all spectrum (1:1) in each tower for LTE, even though customers at the edge will experience degraded performance
* Clearwire plans to re-use spectrum at 1:3 ratio in order to deliver more bandwidth to users at the edge
* Carriers will use caps, data transfer pricing, bans on mobile video, and other limiters to manage supply and demand when spectrum is limited.
* 10% subscribers using 50-60% of the available bandwidth would be an example condition for invoking caps/limits
* Clearwire was the only carrier that stated an intent to support high bandwidth needs of users.

Given these data points, some calculations may shed some light on how well mobile carriers can deliver broadband. Using some bandwidth-generous numbers, let's assume:
* 600 subscribers/tower => 200 subscribers sharing the same bandwidth
* 20Mhz of spectrum/sector * 4.8Mbps/hz => ~100Mbps max to users (some references state 144Mbps downlink max)
* 10% of users generating a significant load (higher than the example given above - 10% using 50-60% being unreasonable)
Result: bandwidth available to end user: ~100Mbps / (10% * 200) = 5Mbps

So, unless my math is off, typical bandwidth performance of WiMAX under a reasonably heavy load (but not extreme) is around 5Mbps. Even if this is off by a factor or 2, users won't get more than 10Mbps under loaded conditions. This compares favorably with other references on practical wireless performance expectations (1). Users may occasionally get up to 100Mbps, but that would be under very ideal circumstances with no other significant traffic.

How much bandwidth is required for Broadband? This is still an open question, though the range seems to be somewhere between 25Mbps and 1Gbps per home, with some common ground around 100Mbps (1). That's more than an order of magnitude higher than WiMAX under loaded conditions.

Bottom line: Wireless internet technologies are very important and will provide great value under many circumstances. It's also clear that more spectrum is required to meet the growing wireless demand. However, wireless technologies cannot provide the broadband services required by critical bandwidth-hungry applications such as telepresence, telemedicine, high definition video, etc. In addition to bandwidth limitations, contention ratios, latency, coverage, and reliability also present significant challenges for wireless internet technologies.

To directly respond to Mr. Bellaria's post, wireless internet technologies can help address adoption challenges by making internet services widely available. However they will not address broadband deployment challenges to the home. Diluting and/or diverting resources and funding away from solutions such as fiber, which can deliver true broadband to the home, would be a serious mistake. The National Broadband Plan must take these wireless limitations into account and set priorities accordingly.

(1) The Initial Report of the U.S. Broadband Coalition recommends 90% availability of a) 100Mbps to 1Gbps to the home and b) 1-10Mbps for wireless internet services by 2015. The report also details a variety of broadband requirements for specific applications. http://www.bb4us.net/index.html

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